Physician's Weekly Article - Screening for Colorectal Cancer

       Newer testing methods have emerged for colorectal cancer, and several healthcare groups have collaborated to update colorectal cancer screening guidelines.

      In 2008, the American Cancer Society, the American College of Radiology, and the U.S. Multi-Society Task Force on Colorectal Cancer released the first-ever joint consensus guidelines for colorectal cancer (CRC) screening. Colorectal cancer is the third most common cancer diagnosed in men and women and the second leading cause of death from cancer. The new guidelines, available online at http://caonline.amcancersoc.org, represent the most current scientific evidence and expert opinion available. “This was the first time that multiple groups have collaborated to produce guidelines to screen for CRC,” explains David A. Lieberman, MD. “In the past, different organizations have produced CRC screening guidelines separately and each has had subtle differences between them. Our goal was to resolve any potentially confusing messages to healthcare providers by coming to a consensus.”

      Assessing Current Technology

      Screening tests for CRC vary depending on several factors, but the guidelines indicate that any one of the available options has the potential to significantly reduce incidence and mortality rates when applied in a systematic program of regular screening. Currently, there is a range of options for CRC screening in the average-risk population aged 50 and older (Table 1). “The current technology falls into two general categories,” Dr. Lieberman says. “The first category is tests, which are primarily early cancer detection tests. These are stool-based tests that detect occult blood or exfoliated DNA. The second category of tests can detect both adenomas and early cancer, with greater potential for cancer prevention. These tests include structural exams, such as flexible sigmoidoscopy [FSIG], colonoscopy, double-contrast barium enema [DCBE], and CT colonography [CTC], also known as virtual colonoscopy.”

      The guidelines state that stool tests are best suited for detecting cancer, but they will also deliver positive findings for some advanced adenomas. Structural exams, on the other hand, can achieve the dual goals of detecting adenocarcinoma and identifying adenomatous polyps. Dr. Lieberman says that “these tests may be used alone or in combination to improve sensitivity. In some instances, they can help ensure a complete examination of the colon if the initial test cannot be completed. The guidelines express a strong preference for screening tests that can detect cancer early as well as precancerous polyps—notably FSIG, colonoscopy, DCBE, and CTC—because they provide a greater potential for cancer prevention through polyp removal.”

      Questions Remain With CTC

      The rationale for including CTC, Dr. Lieberman notes, is that several large studies have been published since 2003 (when the last guidelines were released) indicating that this screening method can detect significant polyps and early cancers at a very high rate. “However,” he says, “CTC is still a relatively new test, and there are many unanswered questions that need to be addressed. More information is needed to determine which patients need to be referred for colonoscopy after they’ve had a CT scan. The current guidelines recommend that all patients with polyps 6 mm or greater should be offered colonoscopy after CT, but there’s debate about doing this in patients with polyps in the 1-to-5 mm range. In addition, it’s important to determine the best way to handle the detection of extra-colonic findings because they could lead to further testing costs and complications.”

      Radiation exposure and repeated exposures to CTC are other issues surrounding use of this screening method for CRC. “Average-risk patients could be at increased risk for more serious developments later in life if they’re exposed to radiation from CT scanning,” Dr. Lieberman says. “Furthermore, more clarity is needed to determine how often these tests should be repeated. The guidelines are conservative and recommend a 5-year interval after negative results, but more evidence is needed to support this recommendation.”

      Ensure Quality Testing

      Regardless of the screening test used to detect CRC, the guidelines stress that the method be selected and performed with high quality. “With each test, there are unique quality indicators that need to be part of the screening program,” says Dr. Lieberman (Table 2). “For example, the tests that are primarily early cancer detection tests are all stool-based exams. These tests need to be repeated on a regular basis—perhaps every year or two—in order for the screening program to be effective. Single, one-time testing misses many patients who have important colonic lesions. It’s important to recognize that noninvasive testing will need to be repeated annually. The screening program will be ineffective if patients aren’t willing to oblige or if physicians don’t have a system in place to provide reminders for these tests. If these circumstances present, other screening methods should be considered.”

      For screenings that involve CT scans, Dr. Lieberman says that the radiology community has adopted a number of quality measures that relate to the reporting of findings. “Any program that uses CT scans should perform quality studies that analyze how well the results correlate with colonoscopy. Several algorithms have been created to help guide physicians. The new guidelines also provide information on aspects of high-quality programs for all screening methods. The hope is that more physicians will become aware of these screening modalities to reduce the burden of CRC.”

      David A. Lieberman, MD has indicated to Physician’s Weekly that he has worked as a consultant for Genenews (Scientific Advisory Board) and has received grants/research aid (in the past 12 months) from AstraZeneca and Novartis.